Q. Consider the following statements:
1. Photic zone is the upper layer of the aquatic ecosystems.
2. In the aphotic zone, only respiration activity takes place.
Which of the statements given above is/are correct?

[A] 1 only

[B] 2 only

[C] Both 1 and 2

[D] Neither 1 nor 2

Answer: C

Explanation: Based on light penetration and plant distribution they are classified as photic and aphotic zones

Photic zone:

  1. It is the upper layer of the aquatic ecosystems, up to which light penetrates and within which photosynthetic activity is confined.
  2. The depth of this zone depends on the transparency of water.
  3. Both photosynthesis and respiration activity takes place.
  4. photic (or “euphotic”) zone is the lighted and usually well-mixed portion that extends from the lake surface down to where the light level is 1% of that at the surface.

Aphotic zone:

  1. The lower layers of the aquatic ecosystems, where light penetration and plant growth are restricted form the aphotic zone.
  2. Only respiration activity takes place.
  3. aphotic zone is positioned below the littoral and photic zones to bottom of the lake where light levels are too low for photosynthesis. Respiration occurs at all depths so the aphotic zone is a region of oxygen consumption. This deep, unlit region is also known as the profundal zone.

Source: Shankar IAS